The disclosed embodiments generally relate to electromagnetic flow meters.
Current insertion flow meters sample small areas of the flow through a pipe. Even those designed for large pipes simply sample several small sections. They then average these readings in an attempt to get an accurate flow measurement. All averages have some sort of weighting; the most common is to give each reading equal weights. Unfortunately, even if positioned such that each sensor has equal annular area, giving each sensor an equal rating does not lead to accurate measurements if the flow varies from that used to calibrate the meter. Giving unequal weightings can lead to accurate readings, but detailed information about the flow profile is required to give these weights. If the flow changes, the meter will be inaccurate. Separate cores require multiple pre-amps. This makes for a cumbersome and costly meter.
Current insertion flow meters also utilize threaded joints in the body of the meter. Threaded joints are at risk for rotation and backing out after installation. Using a threaded joint as part of an electro-magnetic sensor head is challenging because the sensor must maintain alignment after installation and cannot be allowed to rotate. Snap fits prevent axial movement, but not rotation. They are not strong when bending.
In addition, traditional insertion meters trade off two factors with stem design: insertion force and deflection strength. The smaller the stem, the less force is required to install the meter. A thin stem, however, is subject to unwanted deflection, vibration, fatigue, and breakage.
Further, electrode wires in current insertion meters require shielding from their core's electromagnetic field. Typical cores accomplish this by running the electrode wires up the middle of the core where no field is generated. This can be expensive to machine, difficult to install, and adds complexity to the coil winding.
Insertion flow meters are installed into a flow pipe using hot tap adapters that mount onto a ball valve. Traditional hot tap adapters anchor the meter at the top of the adapter event after installation. This is the furthest point from the force of the flow and the longest moment arm. This causes excessive deflection and vibration which negatively affect meter accuracy.
Hand-insertable hot tappable insertion flow meters often have their alignment decoupled from their installation. That is, the meter can be threaded onto the valve fitting and then aligned afterwards. Mechanically assisted hot tappable flow meters, however, are typically locked into the orientation they are installed in. Threading the meter onto the valve fitting determines the angle of the meter to the flow. This means that the installer must often compromise between the correct installation torque of the fitting and the correct angle of the meter to the flow.
Insertion flow meters' accuracy is also dependent on how consistently they are installed. Any difference in installation angle between where the meter was calibrated and where the meter was installed will worsen the accuracy of the meter.
Current Insertion flow meter controllers must compensate for DC offset on electrodes which may be caused, for example, by electrochemical interaction of the electrodes. This decreases the accuracy of the meters. In addition, other insertion flow meters need to utilize precise timing and switching circuitry to read the signals increasing the overall complexity and cost of the meters.